DropShadow on ClipRect

AppScaffold.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class AppScaffold extends StatefulWidget {
  final double offsetSize;

  const AppScaffold({
    @required this.offsetSize,
  });

  @override
  State<StatefulWidget> createState() => _AppScaffoldState();
}

class _AppScaffoldState extends State<AppScaffold> {
  _AppScaffoldState();

  onDragStart(DragStartDetails details) {
    print(details);
  }

  Widget buildMenuWidget(BuildContext context) {
    return Align(
      alignment: Alignment(1, 1),
      child: Icon(
        Icons.menu,
        color: Colors.black,
      ),
    );
  }

  Widget buildBodyWidget(BuildContext context) {
    return CustomPaint(
      painter: MyCustomPainter(
        clipSize: 55,
        blurSize: 4
      ),
      child: ClipPath(
        clipper: MyCustomClipper(clipSize: 55),
        child: Scaffold(
          body: Center(
            child: Text("Test"),
          ),
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
        color: Colors.white,
      ),
      padding: EdgeInsets.fromLTRB(0, 0, widget.offsetSize, widget.offsetSize),
      child: Stack(
        children: <Widget>[
          buildMenuWidget(context),
          buildBodyWidget(context),
        ],
      ),
    );
  }
}

class Paths {
  static Path getMenuClipPath(Size size, double clipSize) {
    var path = Path();
    var bottomRight = Offset(size.width, size.height);
    List<Offset> points = [
      Offset(0, 0),
      Offset(size.width, 0),
      bottomRight - Offset(0, clipSize),
      bottomRight - Offset(clipSize, 0),
      Offset(0, size.height)
    ];
    path.addPolygon(points, true);
    return path;
  }
}

class MyCustomClipper extends CustomClipper<Path> {
  double clipSize;
  MyCustomClipper({this.clipSize});

  @override
  Path getClip(Size size) {
    return Paths.getMenuClipPath(size, clipSize);
  }

  @override
  bool shouldReclip(CustomClipper<Path> oldClipper) {
    return true;
  }
}

class MyCustomPainter extends CustomPainter {
  double clipSize;
  double blurSize;

  MyCustomPainter({this.clipSize, this.blurSize});

  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..color = Colors.black
      ..maskFilter = MaskFilter.blur(BlurStyle.normal, blurSize);

    var path = Paths.getMenuClipPath(size, clipSize);
    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    // TODO: implement shouldRepaint
    return true;
  }
}